▎ 摘　　要

The dynamics of hot phonons in supported, suspended, and gated Monolayer graphene was studied by using time-resolved anti-Stokes Raman spectroscopy. We found that the hot phonon relaxation is dominated by phonon-phonon interaction in graphene, and strongly affected by the interaction between graphene and the substrate. Relaxation via carrier-phonon coupling, known as Landau damping, is ineffective for hot phonons Which are in thermal equilibrium with excited carriers. Our findings provide a basis for better management of energy dissipation in graphene devices.